Conventionally, in lithography to manufacture a semiconductor microdevice such as a semiconductor memory or logic circuit, reduction projection exposure using ultraviolet rays has been performed.
The minimum size that can be transferred by reduction projection exposure is proportional to the wavelength of light used for the transfer and inversely proportional to the numerical aperture of a projection optical system. Hence, in order to transfer a fine microcircuit pattern, light wavelength has been decreased. The wavelength of ultraviolet light is decreased as in mercury lamp i-line (wavelength: 365 nm), a KrF excimer laser (wavelength: 248 nm), and an ArF excimer laser (wavelength: 193 nm).
The feature size of semiconductor devices has been decreasing rapidly, and lithography using ultraviolet light has limitations in dealing with this trend. In order to print a very small microcircuit pattern of as small as less than 0.1 μm efficiently, a reduction projection exposure apparatus which uses extreme ultraviolet light (EUV light) having a wavelength of about 10 nm to 15 nm which is shorter than that of ultraviolet rays has been developed. Accordingly, an EUV light source to supply EUV light to an exposure apparatus is under development as described in Japanese Patent Laid-Open No. 9-320792.
The currently proposed exposure apparatus EUV light source mainly includes two types, i.e., the laser plasma (LPP) type and the discharge (DPP) type.
To transfer a microcircuit pattern, the optical axes of the light source and exposure apparatus must be aligned accurately, and the optical axes that are aligned once should be kept not to displace from each other.
Each of FIGS. 3 and 4 shows the positional relationship among the light-emitting point of a conventionally typical EUV light source, the connecting portion of the EUV light source to an exposure apparatus, the position of the focal point, and the positions of the mirrors of an illumination optical system.
FIG. 3 is a view showing a portion in the vicinity of the connecting portion of an exposure apparatus and a DPP type EUV light source which emits EUV light.
Referring to FIG. 3, reference numeral 1 denotes a light source chamber; and 2, an exposure apparatus chamber. A connecting flange 3 of the light source chamber 1 and connecting flange 4 of the exposure apparatus chamber 2 are fastened and fixed to each other with a hexagonal bolt or the like (not shown). In the light source chamber 1, plasma light emitted from a light-emitting portion 5 is reflected by a multilayered film mirror 6 and focused on a focal point 7 of the connection surface of the two chambers 1 and 2. The focused light diverges again and is reflected by a concave mirror 28 of the exposure apparatus so as to form parallel light.
The light-emitting portion 5 and multilayered film mirror 6 are fixed to a base (not shown) arranged in the light source chamber 1. The mirror 28 of the exposure apparatus is fixed to a base (not shown) arranged in the exposure apparatus chamber 2. The position of the focal point 7 is determined by a focal point aperture arranged in the exposure apparatus chamber 2. Usually, the focal point 7 is set on the connection boundary surface of the light source chamber 1 and exposure apparatus chamber 2, as shown in FIG. 3.
FIG. 4 is a view showing another conventional example which uses an LPP type EUV light source.
Referring to FIG. 4, reference numeral 1 denotes a light source chamber; and 2, an exposure apparatus chamber. A connecting flange 3 of the light source chamber 1 and connecting flange 4 of the exposure apparatus chamber 2 are fastened and fixed to each other with a hexagonal bolt (not shown) or the like. This structure is identical to that of FIG. 3.
In the light source chamber 1, plasma light emitted from a light-emitting portion 5 is reflected by a multilayered film mirror 6 and focused on a focal point 7 of the boundary surface of the light source chamber 1 and exposure apparatus chamber 2.
In the exposure apparatus chamber 2, reference numeral 39 denotes a pair of Schwarzschild-type mirrors. Of the mirrors 39, one convex mirror 39a has a hole which is formed at its center and set on the boundary surface where the light source chamber 1 and exposure apparatus chamber 2 are connected. The hole (aperture) of the convex mirror 39a coincides with the focal point 7. Light focused on the focal point 7 diverges again and is reflected by the other concave mirror 39b, and is reflected again by the convex mirror 39a so as to form parallel light.
The conventional example described above has the following problems. More specifically, the light-emitting portion 5 of the light source, the focusing optical system 6, and the aperture of the focal point 7 are fixed to a support in the light source chamber 1, and a mirror 8 of an illumination optical system is fixed to a support in the exposure apparatus chamber 2. If pressures in the respective chambers fluctuate, the corresponding chambers deform, and the relative positions of optical components which are adjusted in advance may displace.
The aperture to determine the position of the focal point 7 is located on the flange 3, i.e., on the connection boundary surface of the light source chamber 1 and exposure apparatus chamber 2. Therefore, a member to fix the aperture must be set in the flange 3 and is thus difficult to attach.